mid-15c., from present participle of blare. Of things other than sounds, from 1866.

blare

v.

late 14c., bleren "to wail," possibly from an unrecorded Old English *blæren, or from Middle Dutch bleren "to bleat, cry, bawl, shout." Probably echoic, either way. Related: Blared; blaring. As a noun from 1809, from the verb.